Flotation is a physical separation method for separating a mixture of particles on the basis of differences in the particles' surface wettability. In such a method, utilized for example for separating ore minerals and gangue, a gas such as air or nitrogen is introduced with the aid of the aeration device into the particle mixture that is present in the form of an aqueous suspension, the pulp. In addition flotation chemicals for hydrophobizing the surface of the valuable particles, in other words the ore particles in the case of a crude ore, are added to the pulp. The gas bubbles present in the pulp adhere to the hydrophobic particles, thereby producing adducts, also called aeroflocs, which rise to the surface and accumulate as a foam product on the pulp and can be discharged from there.
In order to enable aeroflocs to form it is necessary to induce turbulences in the pulp with the aid of a mixing device, the aforementioned stirrer, so that the gas will be dispersed in the pulp and collisions are able to take place between gas bubbles and particles. However, not every collision leads to the formation of an aerofloc. Thus, forming an adduct from a small gas bubble with a small particle requires a collision taking place with relatively high kinetic energy, i.e. the particle must be accelerated to a high velocity by the mixing device. To achieve this with a stirrer, however, would necessitate at best high expenditure of energy and high material attrition, which would make the flotation process uneconomic. Flotation apparatuses with stirrer as mixing device are therefore operated with lower input of energy in such a way that the hydrodynamic conditions that become established favor the separation of particle fractions having diameters that are larger on average. Due to a lack of sufficient kinetic energy finer particles in this case form at best adducts on a smaller scale and remain behind in the residual pulp. In order to recover the fine fraction of the particles the residual pulp is conventionally treated further in other downstream flotation apparatuses, which is associated with corresponding process engineering and equipment overhead.